1. Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile apparatus, or the like and, more particularly, to an image forming apparatus which optically detects the remaining amount of a developing agent.
2. Related Background Art
As a conventional developing agent presence/absence detection device in an electrophotography apparatus or the like, a light-transmitting type developing agent presence/absence detection device, in which a photointerrupter is formed by arranging a light source and a light-receiving element to oppose each other, and which detects the presence/absence of a developing agent therebetween, is known (Japanese Laid-Open Patent Application No. 63-2087).
FIG. 11 is a sectional view showing a principal part of an example of a light-transmitting type device for detecting the presence/absence of a developing agent. In FIG. 11, the device includes a light-emitting element 101, a light-receiving element 102, and a developing agent container 103, which has windows 104 and 105 for passing light at positions opposing the light-emitting element 101 and the light-receiving element 102.
In this device, while the developing agent container 103 stores a sufficient amount of developing agent D, light emitted from the light-emitting element 101 and entering the developing agent container 103 via the window 104 is interrupted by the developing agent D, and does not reach the light-receiving element 102. On the other hand, when the developing agent container 103 becomes empty upon consumption of the developing agent D, light emitted from the light-emitting element 101 passes through the windows 104 and 105, and reaches the light-receiving element 102. In this manner, the presence/absence of the developing agent D is detected based on a change in output from the light-receiving element 102.
A window cleaning member 106 is pivotally driven by a driving source (not shown) about a rotational shaft 107 as the center of rotation. A cleaning sheet 108 consists of a flexible member, and contacts the inner surface of the window 104 or 105 upon pivotal motion of the window cleaning member 106 to wipe off developing agent D which becomes attached to the inner surface of the window 104 or 105. Thus, the presence of the developing agent can be prevented from being erroneously detected due to developing agent D which becomes attached to the windows and shields light emitted from the light-emitting element 101 although the developing agent container 103 is empty.
In such a light-transmitting type developing agent presence/absence detection device, a drop in detection accuracy due to attachment of dust to a light-emitting portion and a light-receiving portion poses a problem. For example, in Japanese Laid-Open Patent Application No. 2-284165, the light-emitting portion or the light-receiving portion is flexibly held, and is kept in tight contact with the developing agent container. For this reason, dust attachment prevention performance can be improved as compared to a type in which the light-emitting portion and the light-receiving portion are simply fixed. Furthermore, this reference also proposes a mechanism for cleaning the light-emitting portion and the light-receiving portion in synchronism with attachment/detachment of the developing agent container or opening/closing of a door.
However, although the type in which the light-emitting portion or the light-receiving portion is kept in tight contact with the developing agent container is effective in terms of dust attachment prevention, if the light-emitting portion or the light-receiving portion cannot be arranged in tight contact with the developing agent container due to a limitation in the layout of the apparatus, then the effect cannot be expected, as a matter of course. The convey path of a recording medium is the most important limitation in the layout of the apparatus, and is often located near the developing agent container to make the apparatus compact as a whole.
In particular, when the convey path extends just below the developing agent container (immediately therebelow in the vertical direction), the light-emitting portion and the light-receiving portion cannot be arranged immediately below the developing agent container, and must be arranged to avoid the convey path.
In this case, however, the presence/absence of the developing agent in a bottom portion of the developing agent container cannot be detected.
For this reason, upon detection of the absence of the developing agent, some portion of the developing agent still remains on the bottom portion, resulting in an uneconomical arrangement.